Art of producing metallic zinc



v 3 UNITED STATES PATENT OFFICE.

' PARKER O. CHOATE, OF NEW YORK, N. Y., ASSIGNOR TO THE ELECTRICAL ZINCCOMPANY, OF NEW JERSEY.

ART OF PRODUCING METALLIC ZINC.

SPECIFICATION forming part of Letters Patent No. 519,361, dated January9, 1894.

I Application filed January 21,1892. Serial 110.418.5365. (Nospecimens.)

To all whom it may concern.-

Be it known that I, PARKER 0. 0110mm, a citizen of the United States,residing in the city of New York, in the county and-State of New York,have invented certain new and useful Improvements in theArt of ProducingMetallic Zinc, (Case No. 5,) of which the following is a specification.

My invention relates generally to the production of metallic zinc fromits ores and the object of my improvements is to provide an electrolyticsolution of zinc from which a commercially pure metallic zinc may beobtained by means of electrolysis.

While in my process any of the ores of zinc may be utilized in preparingsuch a solution, it is more especially valuable when employed inconnection with that large class of ores known as blendous or complexwhich contain besides zinc numerous other metals such as gold, silver,iron, lead, arsenic, antimony, bismuth, cadmium, &c.,in varyingproportions, and which, on account of the difficulty of working themeconomically have heretofore been discarded at the mines in greatquantities as waste products. In working such ores for the extraction ofmetals other than zinc as heretofore practiced there has been a loss ofthe zinc except when utilized as a pigment, and at the same time itspresence causes heavy losses of the other metals of value such as gold,silver, 850. Although in many cases these ores are very rich in zinc,which is often the most valuable constituent, all attempts to treat themfor the extraction of that metal commercially have failed even at theexpense of the sacrifice of the other constituents of value. Thus theordinary -method of producing metallic zinc from the ore by distillationis entirely inapplicable to these complex ores, since so many othermetals are distilled with the zinc and enter as impurities into themetallic product that it is entirely unfit for the commercial uses towhich metallic zinc is applied. Although numerous attempts have beenmade to that end no method has been heretofore devised'by means of whichit has been possible to continuously produce pure metallic zinc on aprofitable commercial scale,'by electrolytic deposition.

The difficulty in utilizing electrolysis as a means of producing puremetallic zinc is pri marily due to the fact that zinc is electropositiveto many of the metals which are present with it in the ore and so muchso that it will deposit upon itself or precipitate most of these metalsfrom an acid solution in which they are present. Consequently if suchmetals are allowed to be present in the bath in solution with the zincthey will be deposited with it and appear as impurities in the product.It is evident therefore that before the deposition of pure zinc from anelectrolytic solution can be begun the solution must be free from allthose substances which would be deposited before or along with the zinc.

Attempts have heretofore been made to purify impure solutions of zinc byremoving the metals other than zinc therefrom by the use of chemicalprecipitants. The precipitation of other metals from a'solution in whichthey are present with zinc, so as to obtain a pure solution of zinc is,however, extremely difficult, even as alaboratory experiment, and hasproven utterly impracticable on a commercial scale.

While it might appear that an impure solution of zinc could be readilybrought to the requisite degree of purity, at the expense of the loss ofa small quantity of impure zinc, by passing an electric current throughthe solution, until all the depositable impurities were deposited out,this is not in fact the case, since in depositing zinc and other metalsfrom solutions of their salts, free acid quickly appears in the baththrough the action of the current upon the solution, which, unlessneutralized or annulled, re-dissolves the deposited metals from thecathode as fast as they are deposited thereon thus keeping a percentageof them always in the solution. This difiiculty cannot be obviated byannulling the free acid with the zinc ore since in so doing theimpurities contained in the ore would continually enter the solutiontaking the place of those deposited or precipitated out by the current.By my invention I overcome all these difficulties and produce anelectrolytic solution of zinc free from depositable impurities, usingthe electric current as the purifying agent since the condition in whichI take the zinc wherewith to neutralize the acid set free in the bathduring the process of puritication enables me to do so withoutintroducing additional soluble impurities into the bath.

From the point of view of my process only those substances which wouldenter into solution with the zinc in a zinc electrolyte and be depositedtherefrom before or along with the zinc by the electric current underthe conditions used, are regarded as impurities. To the end therefore ofobtaining a commercially pure metallic zinc my invention consists inproducing a pure electrolytic solution of zinc by passing an electriccurrent through an impure solution of zinc salts to deposit andprecipitate out the depositable impurities and neutralizing the freeacid liberated in the bath with an oxidized zinc fume freed from itssoluble depositable impurities.

Any usual or suitable mode may be adopted for obtaining the zinc oxideto be used in my process. As an example of one well known method, theore may be first crushed and then when it contains an excess of sulphur,it may be roasted at a moderate temperature not sufficiently high tovolatilize the zinc in order to drive off the excess of sulphur. Thepartially desulphurized ore may then be mixed with carbonaceous fuel,such as coal screenings, and roasted in a furnace into which air isadmitted beneath its grate at a temperature high enough to volatilizethe zinc until the zinc contained in the ore is driven off. Thevolatilized zinc and other volatilized bodies may then be caught andcollected in a bag room in the ordinary manner. The resulting productwill be substantially pure oxide of zinc in the shape of a fine powderknown as fume mixed with such lead as was contained in the ore and whichis volatilized with the zinc. There may also frequently occur with thezinc and lead fume, as condensed products, other volatilizable oxideswhich may have been present in the ore in their metallic form such asthe oxides of antimony, arsenic, bismuth, cadmium, &c. These substancesare all volatilizable at a lower temperature than zinc and lead. Hencewhen they occur in appreciable quantities I dispose of them bysubjecting the fume to a moderate roast at a temperature of from 500 to800 Fahrenheit in any well known form of muflie furnace, thereby drivingthem off, care being taken not to apply sufficient heat to revolatilizeany of the zinc or lead contents. By means of this roast the fume ispurified from its more volatile constituents, thereby easily eliminatingall those soluble depositable impurities which would otherwise enterinto solution with the zinc when the fume is used to neutralize the freeacid in the electrolytic bath.

Other metals which may have been contained in the ore, such as iron,gold, silver, copper, nickel, &c., are not primarily driven off with thezinc and lead but remain in the furnace in the form of cinder or slagand may afterward be smelted out and recovered in the usual manner.

I do not confine myself to the above described mode of producing orpurifying the zinc oxide, as this may be done in any suitable way, itbeing only necessary to my invention that I should have for use in myprocess an oxide of zinc which has been properly purified from itslighter soluble impurities.

The impure zinc solution to be treated for the production of the pureelectrolyte may be one primarily prepared in any convenient or usualmanner, as by treating a zinc ore or the impure flue product from a zincvolatilizing furnace with a solvent of the zinc constituent.

The impure solution is placed in a tank or vat and current from asuitable source of electricity, as a dynamo electric machine is passedthrough it. The density of the current applied in purifying the solutionmust be at least equal to and should preferably be somewhat greater thanthat of the current which it may be desired to apply afterward in thedeposition of pure metallic zinc.

On the application of the current some'of the depositable impurities inthe bath will be deposited upon the cathode while the others through theaction of the current and of the secondary reactions which will takeplace will be thrown down as precipitates in the bath.

In order to prevent the redissolving of the deposited and precipitatedimpurities, the free acid liberated in the bath by the action of thecurrent is neutralized by means of the oxidized zinc fume abovedescribed. For this purpose the fume maybe introduced directly into thebath in sufficient quantities to keep the solution neutral, or the freedacid, which will rise to the top of the bath may be continuously drawn0E into a separate tank and after being neutralized with the fume bereturned to the depositing tank. In case the zinc solvent used in makingup the solution be also a solvent of lead, which will be the onlyimpurity associated with zinc in the fume, enough sulphuric acid shouldbe introduced into the bath, when lead is present in the fume, to renderit insoluble. With this precaution any desired solvent of zinc may beused in making up the solution. The application of the current to thesolution should be continued until all the depositable impurities aredeposited or precipitated when the precipitates may be allowed to settleand the clear solution to be drawn ofi: ready for use. In this manner,since by the use of the oxidized zinc fume the free acid liberated inthe bath may be neutralized without introducing additional impurities. Iam able to produce from a very impure solution of zinc a neutral zincelectrolyte of such nature that it will yield upon electrolysis acommercially pure metallic zinc. The zinc may be deposited from such asolution by means of electrolysis using an insoluble anode, as one ofcarbon, and a cathode of suitable material such as zinc or copper, andthe process maybe rendered continuous by maintaining and regeneratingthe solution by neutralizing or annulling the free acid liberated in thebath with an oxidized zinc fume free from its soluble depositableimpurities such as is hereinbefore described. I do not however claimherein the method of doing this as I have made it the subject of anotherapplication for Letters Patent filed of even date herewith.

The advantages of my invention will be readily apparent to those skilledin the art since by means of it the most impure ores of zinc, which havehitherto been discarded as waste products can be utilized in theproduction of a zinc electrolyte free from all depositable impuritiesfrom which a commercially pure metallic zinc can be obtained.

What I claim as new, and desire to secure by Letters Patent, is-

1. The hereinbefore described process of producing from an impuresolution of zinc salts, a zinc electrolyte free from depositableimpurities, which consists in subjecting the solution to the action ofan electric current to precipitate and deposit the depositableimpurities and neutralizing the acid set free in the bath with anoxidized zincfume freed from its more volatile soluble constituents,substantially as set forth.

2. The hereinbefore described method of producing from an impuresolution of zinc salt-s a zinc electrolyte free from depositableimpurities which consists in subjecting the solution to the action of anelectric current to precipitate and deposit the depositable impuritiesand at the same time preventing the re-solution of such impurities inthe solution by neutralizing the acid set free in the bath with aneutralizing agent which is free from any depositable impurities solublein the solvent element of the bath, substantially as set forth.

In testimony whereof I have hereunto subscribed my name this 16th day ofJanuary, A.

PARKER G. CHOATE. Witnesses:

BENJAMIN BARKER, J r., CLARKSON A. CoLLINs.

